An assembly device disclosed in JP 10-45065 A (U.S. Pat. No. 6,038,767) is known as a device for automatically assembling a swash plate-type fluid machine, for example, a swash plate-type compressor. In this assembly device, pistons are sequentially incorporated with a swash plate of a swash plate-equipped shaft that is rotatably supported in a horizontal posture, to thereby assemble a shaft assembly. Each of the pistons is then supported by a cylinder disposed on both axial sides thereof, so the circumferential position of each of the pistons is held. In this state, the shaft assembly is incorporated into a cylinder block.    Patent Document 1: JP 10-45065 A